1. Field of the Invention
The present invention relates to single-phase induction motors, and more particularly, to a single-phase induction motor and a method for reducing noise in the same, which minimize noise and vibration by balancing the magnetomotive forces of stator windings in the motor.
2. Description of the Related Art
A single-phase induction motor is a type of alternating current “AC” motor. The simplest configuration of the single-phase induction motor uses commercial power without alteration and includes a single-phase main winding provided in a stator and a squirrel-cage shaped conductor provided in a rotor. Since the motor is not rotated with commercial power alone, a shading coil is installed, or a split-phase coil or a capacitor is installed in an auxiliary coil to start the motor. Single-phase induction motors are classified based on their structure into capacitor split-phase motors, resistance split-phase motors, capacitor-run motors, shading-coil motors, and reactor motors.
Among the different types of single-phase induction motors, the capacitor-run motor has a main winding, an auxiliary winding connected in parallel with the main winding, and a capacitor connected in series with the auxiliary winding. The capacitor-run motor is started using the auxiliary winding and the capacitor. When in operation, the capacitor-run motor does not disconnect the auxiliary winding, but instead allows current to flow through the auxiliary winding so as to lag current flowing through the main winding by 90 degrees.
In the capacitor-run motor, the auxiliary winding is spatially displaced at 90 degrees to the main winding in the stator, and is electrically connected in parallel to the main winding. Current flowing through the main and auxiliary windings is split into two phases by causing an impedance difference between the main and auxiliary windings using the capacitor connected in series with the auxiliary winding. Correct phase splitting must be performed (i.e., complete phase equilibrium must be established) for the rotating magnetomotive force produced by the split-phase stator windings.
If incorrect phase splitting is performed, the rotating magnetomotive force rotates while rippling. If a ripple is present in the rotating magnetomotive force, torque ripple occurs in the rotor, causing noise and vibration in the motor.
The conventional single-phase induction motor controls its rotation speed through tap adjustment of the stator windings. In this conventional motor, even if phase equilibrium is established in a certain running range of the motor, the phase equilibrium is broken causing noise and vibration if a tap in the stator windings is switched to select a different running range.
In addition, even if phase equilibrium is established under a condition where no load is present, the phase equilibrium is broken under a condition where a load is present, due to characteristics of the single-phase induction motor, so that vibration and noise occurs in actual operation of the motor.